Cerebral ischemia (or brain ischemia) is a deficiency of blood supply to the brain. Cerebral ischemia can be caused by events such as cardiac arrest, traumatic brain injury, stroke, near drowning, birth asphyxia, drug overdose, and hypoxic encephalopathy. Cerebral ischemia can cause brain damage even if blood flow is restored to the brain, and such brain damage can occur after restoration of blood flow to the brain. For example, a component of brain damage from cardiac arrest may not appear to be histologically apparent for approximately 24 to 48 hours after resuscitation from cardiac arrest. This delayed brain damage is due to reperfusion disease (i.e., activation of pathological cascades that promote toxic free radical production, release of excitatory amino acids, severe acidosis, and other cellular and molecular changes).
A relatively new therapy for decreasing brain damage from cardiac arrest and other causes of cerebral ischemia is inducing mild hypothermia. The sooner hypothermia is induced after reperfusion, the more effective the therapy is in reducing brain damage (see, e.g., Coimbra et al., Moderate hypothermia mitigates neuronal damage in the rat brain when initiated several hours following transient cerebral ischemia, Acta. Neuropath., 1994, 87:325-331; The Hypothermia After Cardiac Arrest Study Group, Mild therapeutic hypothermia to improve the neurologic outcome after cardiac arrest, New Engl. J. Med., 2002; 346: 549-556; and Bernard et al., Treatment of comatose survivors of out-of-hospital cardiac arrest with induced hypothermia, New Engl. J. Med., 2002; 346: 557-563).
The most common method of inducing hypothermia is by the external application of ice. However, conductive cooling is a slow and inefficient method for promoting heat loss (see, e.g., Xu et al., A mathematical model for human brain cooling during cold-water near-drowning. J. Appl. Physiol., 1999, 86:265-272). Another way of inducing hypothermia after cardiac arrest is by performing a cardiopulmonary bypass. However, such a procedure cannot be initiated rapidly or outside of a hospital environment (see, e.g., Tisherman et al., Future directions for resuscitation research. V. Ultra-advanced life support. Resuscitation 1997; 34:281-93).
It would be advantageous to provide methods of treating cerebral ischemia that are less invasive than conventional procedures and can induce hypothermia more rapidly than conventional procedures.